A construction machine, such as a hydraulic excavator, includes a plurality of hydraulic actuators and can drive the hydraulic actuators to move various components, such as booms, arms, buckets, swivel devices, and travel devices, thereby performing various work, and the like. The plurality of actuators are connected to a variable displacement pump and are driven by a pressure liquid discharged from the variable displacement pump. The variable displacement pump is, for example, a swash plate pump or a bent axis pump and can change the tilting angle of a swash plate or axis to change a discharge flow rate of the pressure liquid. The variable displacement pump is provided with a tilting angle control device configured to adjust the tilting angle in accordance with the operation amount of an operation lever of the tilting angle control device.
When the operation amount of the operation lever of the tilting angle control device is maximized, the variable displacement pump discharges the pressure liquid, the discharge flow rate of which is maximum. It is preferable that the maximum discharge flow rate of the variable displacement pump be set so as not to exceed an allowable maximum flow rate of each of all the hydraulic actuators. However, there is a case where a high flow rate variable displacement pump is provided so as to correspond to the hydraulic actuator having the highest allowable maximum flow rate. In this case, the discharge flow rate of the variable displacement pump needs to be controlled accurately in accordance with each of the allowable maximum flow rates of the hydraulic actuators.
The travel devices are separately arranged at both left and right sides of a car body and respectively include separate hydraulic motors. The hydraulic motors are respectively supplied with the pressure liquid from separate variable displacement pumps. The straight running stability deteriorates if the discharge flow rates of the two variable displacement pumps are not accurately controlled.
For example, according to the hydraulic excavator, the flow rates respectively required by the hydraulic actuators differ from one another depending on work conditions, such as excavating work and swiveling work. Therefore, it is desirable that the variable displacement pump discharge the pressure liquid, the flow rate of which is required depending on each work condition of the hydraulic excavator. In this case, the discharge flow rate of the pressure fluid discharged from the variable displacement pump needs to be accurately controlled by the tilting angle control device.
As above, the control accuracy of the tilting angle control device is demanded, and as devices each of which satisfies this demand of the control accuracy, for example, tilt control devices described in PTLs 1 and 2 are known.
The tilting angle control device described in PTL 1 includes a hydraulic regulator (tilt adjustment mechanism) and adjusts the tilting angle of the variable displacement pump in such a manner that a control unit of the tilting angle control device drives the hydraulic regulator. The control unit controls the regulator based on a command value and actual measurement value of the tilting angle and the discharge pressure of the variable displacement pump. According to the tilting angle control device described in PTL 2, the control unit adjusts the tilting angle of the variable displacement pump based also on the temperature of the operating oil.